In the preparation of polyurethane foam carpeting underlayment composites, a widely used composite comprises a polyurethane foam which has been coated on one side with a polyolefin film which acts as a slip surface to allow the carpet to be easily stretched over the underlay. The polyolefin is normally in contact with the undersurface of the carpet. If the carpeting catches fire, the polyolefin component of the underlayment composite acts as a fuel to spread the fire throughout the carpet and underlayment material. Since flame retardants are, in general, incompatible with polyolefins, it has been found necessary to provide other means for flame retarding the carpet underlayment material other than by flame retarding the polyolefin component. Accordingly, the main objective of this invention is to provide a flame retardant composition which, when added to the polyurethane component of a polyurethane/polyolefin composite carpet underlay, acts to prevent or retard flammability of the polyolefin component.